JP5809542B2 - Sputtering target material and manufacturing method thereof - Google Patents

Description

  The present invention relates to a sputtering target material composed of a zinc oxide sintered body and a method for producing the same. A sputtering target is used when forming the transparent conductive film used for transparent electrodes, such as a solar cell and a touch panel, by sputtering method.

  In recent years, a zinc oxide transparent conductive film having high transparency, conductivity and chemical stability at low cost has attracted attention. As a method for forming a zinc oxide-based transparent conductive film, a sputtering method is most suitable, in which a dense and good film quality can be easily obtained, and various zinc oxide sintered bodies used for sputtering target materials have been studied.

For example, Patent Document 1, density ^{5.6g / cm 3 ~5.77g / cm 3} , Shoyuitsubu径2Myuemu～50myuemu, maximum dispersion aggregate diameter of the aluminum component is 5μm or less, the content of aluminum in the aluminum oxide basis An aluminum-doped zinc oxide sintered body having a resistivity of 0.5% by weight or more and a resistivity of 1 × 10 ⁻² Ωcm or less is disclosed.

Patent Document 2 discloses that a target of a composite oxide sintered body produced from a mixed powder composed of zinc oxide and aluminum oxide has a resistivity (specific resistance) of 3 mΩ · cm or less and a sintered density of 5 It is described that the number of abnormal discharges can be reduced at the time of sputtering film formation and generation of particles can be suppressed because of 0.4 to 5.6 g / cm ³ .

  In Patent Document 3, the zinc oxide-based sintered body target contains one or more Group III elements in the periodic table, the relative density is 97% or more, and the surface roughness Rmax of the sputter surface is 3.0 μm. From the following, it is described that arcing is prevented from occurring when power is input for a long time.

In Patent Document 4, by using a dopant powder having a secondary (aggregation) particle size of 2 μm or less as the secondary (aggregate) particle size of the aluminum oxide powder, the sintered particle size is 2 μm to 50 μm at a density of 5.6 g / cm ³ or more. It is described that a high-density sintered body having a maximum dispersion agglomeration diameter of 5 μm or less can be obtained, and that when such a sintered body is used as a sputtering target, a low-resistance film can be obtained.

JP-A-7-258836 JP 2010-270004 A JP 2000-178725 A Japanese Patent No. 3864425

  As described above, various zinc oxide sintered bodies used for the sputtering target material have been proposed, but it cannot be said that the proposed zinc oxide sintered body can reliably prevent abnormal discharge during sputtering.

  For example, although the aluminum-doped zinc oxide sintered body described in Patent Document 1 has low resistance, it is unclear whether abnormal discharge can be suppressed. In addition, the structures of the targets described in Patent Documents 2 to 4 are not sufficiently clarified, and a stable effect is not always obtained.

  This invention is made | formed in view of such a situation, and it aims at providing the sputtering target material which can prevent the abnormal discharge during sputtering stably by the specific composition, and its manufacturing method.

(1) In order to achieve the above object, the sputtering target material of the present invention is a sputtering target material made of a zinc oxide sintered body, and has a density of 5.4 × 10 ³ kg / m ³ or more and 5.6. × 10 ³ kg / m ³ or less, containing 1 wt% or more and 3 wt% or less of Al in terms of Al ₂ O ₃ , the particle diameter of ZnAl ₂ O ₄ particles present in the zinc oxide particles is 3 μm or less, The diameter of ZnAl ₂ O ₄ particles present in the zinc oxide grain boundary is characterized by being 10 μm or less.

Thus, the sputtering target made of the zinc oxide sintered body of the present invention has a density of 5.4 × 10 ³ kg / m ³ or more and 5.6 × 10 ³ kg / m ³ or less, and has a slight void. Since it is a dense sintered body, cracks during sputtering can be prevented while reducing the number of discharges. Moreover, since it contains 1 wt% or more and 3 wt% or less of Al in terms of Al ₂ O ₃ , the volume resistivity can be reduced to 1 × 10 ⁻⁴ Ωm or less. The particle size in the zinc oxide particles have the following ZnAl ₂ O ₄ particles 3 [mu] m, since the particle size in the ZnO grain boundaries have the following ZnAl ₂ O ₄ particles 10 [mu] m, heterogeneous phase of resistance was reduced , Abnormal discharge starting from ZnAl ₂ O ₄ particles can be prevented.

(2) Further, the sputtering target material of the present invention is characterized in that the zinc oxide grain boundary has a Zn—Al—O compound in which the molar ratio of Zn is larger than the molar ratio of Al. Accordingly, since the amount of ZnAl ₂ O ₄ particles can be reduced, thereby preventing the abnormal discharge which starts this.

  (3) Moreover, the manufacturing method of the sputtering target material of this invention is a manufacturing method of the sputtering target material which consists of a zinc oxide-based sintered compact, Comprising: Zinc oxide powder with a purity of 99.0% or more and purity 99.0% The step of mixing the above alumina powder, the step of producing a molded body having a density of 50% or more of the theoretical density using the mixed powder, and the molded body at 1350 ° C. or higher and 1550 ° C. or lower for 10 hours or longer. And the step of firing, wherein the rate of temperature decrease from the firing temperature to 1000 ° C. is 50 ° C./h or more.

This reduces the ZnAl ₂ O ₄ particles contained can be produced sputtering target made of sufficient density zinc oxide sintered body. As a result, it is possible to manufacture a sputtering target that is difficult to abnormally discharge. Moreover, since it presupposes mixing of a zinc oxide powder and Al powder, a sputtering target can be manufactured in large quantities cheaply.

According to the present invention, the particle size in the zinc oxide particles have the following ZnAl ₂ O ₄ particles 3 [mu] m, since the particle size in the ZnO grain boundaries have the following ZnAl ₂ O ₄ particles 10 [mu] m, nonuniformity in resistance The phase can be reduced, and abnormal discharge starting from ZnAl ₂ O ₄ particles can be prevented.

It is a trace figure of the SEM photograph which shows the surface of the sputtering target material of this invention. It is a figure which shows an experimental result.

  Various investigations have been made so far on the suppression of abnormal discharge during DC sputtering of a zinc oxide target material. The present inventors have found that discharge can be suppressed by controlling the structure of the zinc oxide target material. Embodiments of the present invention will be described below.

(Configuration of sputtering target material)
The sputtering target material (hereinafter referred to as sputtering target material) of the present invention is formed of an Al-doped zinc oxide sintered body. The amount of Al added during the production of the sputtering target material is 1% by weight or more and 3% by weight or less in terms of Al ₂ O ₃ . If the amount of Al added is 1% by weight or less, it is difficult to reduce the resistance of the sputtering target material. If the resistance is not low, Zn and Al atoms are not scattered by DC sputtering. On the other hand, if the amount of Al to be added exceeds 3% by weight, ZnAl ₂ O ₄ is excessively increased, abnormal discharge is likely to occur, and the resistance of the film is likely to be uneven. A zinc oxide (ZnO) target material having a stable resistance value of 10 ⁻⁴ Ω · m or less can be obtained by adjusting the amount of Al to be added to 1 wt% or more and 3 wt% or less.

The density of the sputtering target material is 5.4 × 10 ³ kg / m ³ or more and 5.6 × 10 ³ kg / m ³ or less. When the density is less than 5.4 × 10 ³ kg / m ³ , even if the structure is controlled, it does not contribute much to the decrease in the number of discharges. On the other hand, when the density exceeds 5.6 × 10 ³ kg / m ³ , there is no void at all, and the sputtering target material is easily cracked during sputtering.

  The surface becomes several hundred degrees during sputtering, but the opposite surface is bonded to the backing plate and cooled, and thus a temperature gradient is generated in the sputtering target material. For this reason, a difference in thermal expansion occurs, and cracking easily occurs. However, if the density is too high, so-called “escape” disappears, and cracking easily occurs. The surface roughness of the sputtering target material is preferably smaller. The surface roughness is preferably 2 μm or less in terms of Ra (arithmetic average surface roughness).

The particle size of the zinc oxide particles mainly constituting the sputtering target material is preferably 10 μm or more. A larger sintered particle diameter of zinc oxide is preferable, which can reduce the grain boundary and reduce the non-uniform phase of resistance. ZnAl ₂ O ₄ particles exist in the zinc oxide particles and the grain boundaries. The particle diameter of ZnAl ₂ O ₄ particles present in the zinc oxide particles is 3 μm or less, and the diameter of ZnAl ₂ O ₄ particles present in the zinc oxide grain boundaries is 10 μm or less. This reduces the heterogeneous phase in the resistance of the sputtering target material in the composition, it is possible to prevent the abnormal discharge starting from the ZnAl ₂ O ₄ particles.

It is preferable that a Zn—Al—O compound having a Zn molar ratio larger than the Al molar ratio is present in the zinc oxide grain boundary. The Zn—Al—O compound is produced by changing a part of ZnAl ₂ O _{4 into} a Zn—Al—O compound in which the molar ratio of Zn is larger than the molar ratio of Al during firing. This reduces the ZnAl ₂ O ₄ itself, abnormal discharge of the sputtering target material is reduced.

(Method for producing sputtering target material)
As a raw material for the sputtering target material, it is preferable to use high-purity zinc oxide powder. Its purity is preferably 99.0% or higher.

  It is preferable to use a zinc oxide powder having a primary particle size of 500 nm or less. The zinc oxide powder is preferably produced by the French method. The raw material produced by the French method is more likely to be doped with Al and lower in resistance. From the relationship between the average particle diameter and the specific surface area, it is considered that when the slurry is made, the secondary particles are easily loosened and Al is easily dispersed.

The alumina powder (Al ₂ O ₃ powder) preferably has a primary particle diameter of 1 μm or less. This facilitates doping of zinc oxide with Al. In that case, fine α-Al ₂ O ₃ is preferable. The purity of alumina is important and is preferably 99.0% or more.

  In the case of dry molding, a predetermined amount of a dispersant, a binder, and a solvent are added to the raw material powder, followed by ball mill mixing. Then, the obtained slurry is dried by spray drying and granulated. A molded product is produced from this using a die press and CIP. At this time, the density of the compact is set to 50% or more of the theoretical density. This is because the sintered body does not have a relative density of 95% or more when pressureless firing is performed on a molded body of less than 50%. In addition, it is more preferable to set it as 55% or more.

  In the case of wet forming, it can be similarly slurried and formed by casting. The density of the molded body at this time is also set to 50% or more of the theoretical density. In addition, it is more preferable to set it as 55% or more. The binder used for molding is not particularly limited, and known materials such as polyvinyl alcohol and acrylic emulsion can be used. For the dispersant, a general material such as polycarboxylic acid can be applied.

  In either method, preparation of the slurry is important, and viscosity management is particularly important. About each powder, it is desirable to perform preliminary mixing and to perform main mixing. The mixing of the slurry of this mixing is performed until the viscosity does not change for 12 hours or more.

  The viscosity decreases as the mixing time increases. This is because the secondary particles of zinc oxide powder and alumina powder are loosened. If sufficiently loosened, the particles are uniformly dispersed and the viscosity is stable. At this time, it is desirable to use a resin ball because it is necessary to prevent contamination of impurities. For example, the use of alumina balls is more efficient, but in that case, the alumina balls are worn out and mixed into the slurry, which may result in a composition different from that of the slurry.

  Firing is preferably performed under the following conditions. The heating rate is preferably 60 ° C./h or more. The baking temperature is 1350 ° C. or higher and 1550 ° C. or lower and baking is performed for 10 hours or longer. The temperature lowering rate is 50 ° C./h or more from the firing temperature to 900 ° C.

  It is desirable that the atmosphere be fired in air, preferably while introducing a certain amount of Air. It is desirable to use an electric furnace as the atmospheric furnace. This is because the tendency of reduction firing becomes stronger in a gas furnace. Firing in a reducing atmosphere is not preferred.

  When the sintering temperature exceeds 1550 ° C., the sublimation of zinc oxide becomes intense and it becomes difficult to densify. When the sintering temperature is less than 1350 ° C., the sintering itself does not progress so much, and it becomes difficult to obtain a structure that can stably prevent abnormal discharge during sputtering as described above. The firing time is preferably 10 hours or more. If it is less than this, it becomes difficult to obtain the above structure. The upper limit is about 30 hours. Zinc oxide undergoes sublimation at the same time as sintering. If the firing time is too long, a large amount of evaporation occurs on the surface, which increases the amount of processing after firing. Under these conditions, the zinc oxide target material having the above structure can be obtained.

(Inhomogeneous tissue resistance)
Uneven tissue resistance contributes to abnormal discharge. From such a viewpoint, it is preferable that the sintered oxide particle diameter of zinc oxide is large because the grain boundary is reduced and the non-uniform phase of resistance is reduced. Further, the resistance of ZnAl ₂ O ₄ is higher than that of Al-doped zinc oxide. Since abnormal discharge tends to become a starting point is ZnAl ₂ O ₄ particles, the particle size of ZnAl ₂ O ₄ is smaller good, good 10μm or less. Therefore, it is preferable to reduce ZnAl ₂ O ₄ .

Since ZnAl part of ZnAl ₂ O ₄ by the above production method to reduce the ₂ O ₄ molar ratio of Zn is changed to a molar ratio greater than ZnAl-O compound of Al, ZnAl ₂ O ₄ itself is reduced, and abnormal discharge of the sputtering target material is reduced.

In order to produce this compound, the temperature lowering rate during firing is effective. The rate of temperature decrease from the firing temperature to 1000 ° C. is desirably 50 ° C./h or more. Interface ZnAl ₂ O ₄ and zinc oxide is considered a liquid phase is generated, resulting in precipitated slowly when cooled and ZnAl ₂ O ₄ zinc oxide as it is. By lowering the temperature at 50 ° C./h or higher, it is considered that the Zn-rich Zn—Al—O compound is precipitated. This lowers the resistance of the entire sputtering target material, and is presumed to contribute to the reduction of the starting point of abnormal discharge (ZnAl ₂ O ₄ particles).

  Since the Zn—Al—O compound is difficult to detect by XRD, it is presumed that it is close to amorphous. The faster the temperature drop rate, the better for the formation of the Zn—Al—O compound. However, if it is too fast, the sintered body will break due to thermal shock. Since this crack depends on the shape, the temperature drop rate can be appropriately adjusted according to the shape of the sintered body.

  In order to produce an Al-doped zinc oxide sintered body, it is industrial to produce a mixture of zinc oxide powder and aluminum oxide powder, which is suitable for mass production at a low cost. Although pre-Al-doped zinc oxide powder is available, it is expensive and not industrially suitable.

  As a backing plate to which a sputtering target material made of a zinc oxide sintered body is bonded, a copper plate is preferable because it is excellent in heat conduction. In addition to the copper plate, a metal-ceramic composite material using aluminum alloy or copper as a matrix metal and ceramic as a reinforcing material is also suitable. Indium bonding is suitable for the bonding between the backing plate and the sputtering target material made of the zinc oxide sintered body. However, the bonding layer formed of indium desirably has a contact area of at least 90% with respect to the bonding surface of the backing plate and the target material. If the sputtering target material of the present invention and a copper plate are joined with indium and the contact area is 90% or more, cracks due to thermal stress during production or use can be eliminated.

(Example)
Next, sample No. 1 to 24 sputtering target materials were prepared, and the presence or absence of a Zn—Al—O compound and the number of discharges by sputtering were measured for the samples. As raw material powders, a zinc oxide powder having a primary particle size of 300 nm and an alumina powder having a primary particle size of 600 nm prepared by the French method were prepared. A binder was added to each of the raw material powders, and mixed for 6 hours in a resin pot container together with Φ15 and Φ25 resin balls as a mixing medium (preliminary mixing). Thereafter, the two slurries of zinc oxide powder and alumina powder were combined and wet mixed for 30 hours. However, Sample No. Only 3, 11, 19 used alumina powder having an average particle size of 1.2 μm. Sample No. 4, 12, and 20, after the preliminary mixing, the two slurries were mixed together for 4 hours each.

  At this time, the viscosity was measured at the time of 10 hours, 15 hours, 20 hours, and 30 hours from the start of mixing, and it was confirmed that the respective viscosities at 15 hours, 20 hours, and 30 hours were constant. The mixed slurry was taken out, and granulated powder was produced by spray drying. CIP molding was performed using the obtained mixed powder, and a green body was produced with a raw processing allowance of 10 mm. Thereafter, the molded body was fired at 1500 ° C. for 15 hours to obtain a sintered body.

  In this way, a plate-like sintered body of 110 × 110 × 9 mm was produced. This was cut and ground to produce an abnormal discharge evaluation sample of 100 × 100 × 6 mm. Further, using the mill ends, microstructure evaluation, density and volume resistivity were measured by SEM / EDX and XRD. The volume resistivity was measured by the 4-terminal method, and the density was measured by the Archimedes method.

A 100 × 100 × 6 mm plate-like Al-doped zinc oxide sintered body was indium bonded to a copper backing plate. The average particle size of the sintered body was obtained from the intercept method by mirror-polishing the surface of the sintered body and then subjecting the polished surface to thermal corrosion to precipitate crystal grain boundaries, followed by SEM observation. Which particles of ZnO, ZnAl ₂ O ₄ , and Zn—Al—O compound (Zn> Al) in the structure were determined by EDX attached to the SEM.

FIG. 1 is a trace view of an SEM photograph showing the surface of a sputtering target material. As shown in FIG. 1, the average particle diameter of the zinc oxide particles 10 is 10 μm or more. Black region shown in FIG. 1 is a ZnAl ₂ O ₄ particles 20, in the zinc oxide grain boundaries is formed ZnAl ₂ O ₄ particles of about 5 [mu] m, ZnAl ₂ about a number of 1μm in the zinc oxide particles O ₄ Particles are formed. Further, the gray region shown in FIG. 1 is the Zn—Al—O compound 30, and particles of the Zn—Al—O compound 30 are formed at the zinc oxide grain boundary.

  The maximum height Rz was measured with a contact-type surface roughness measuring instrument. The arithmetic average surface roughness Ra of the main surface was all 0.5 μm or less. This was bonded with a copper backing plate and indium to obtain a sputtering target.

  The obtained sputtering target material was used in a DC magnetron sputtering apparatus. Sputtering was performed in a pure argon atmosphere, a pressure of 0.5 Pa, and an input power of 100 W. During sputtering, the backing plate was extracted with cooling water so that the backing plate was kept at 30 ° C. or lower. Abnormal discharge was evaluated by counting the number of arcing that occurred during film formation and counting per unit time (count / h).

FIG. 2 is a diagram showing experimental results. As shown in FIG. In Nos. 1 to 8, Al ₂ O ₃ was added in an amount of 1% by weight, sample No. Nos. 9 to 16 are those in which the addition amount of Al ₂ O ₃ is 2% by weight, sample No. In Nos. 17 to 24, the amount of Al ₂ O ₃ added is 3% by weight. The table in FIG. 2 shows, from the right column, the firing temperature at the time of production, the firing time, the temperature drop rate, the particle diameter of zinc oxide, the particle diameter of ZnAl ₂ O ₄ in the zinc oxide particles and the zinc oxide grain boundary, Zn—Al—O. The presence / absence of a compound and the number of discharges are shown. Sample No. 1-8, Sample No. 9-16, Sample No. About 17-24, the sintered compact was produced from the same raw material granule, respectively. The average particle diameter of the Al raw material was 1.2 μm for all the samples.

From the whole of FIG. 2, it can be seen that the smaller the amount of Al ₂ O ₃ added, the smaller the number of discharges. The particle diameter of the ZnAl ₂ O ₄ particles present in the zinc oxide particles in 3μm or less, the sputtering target material size of ZnAl ₂ O ₄ particles present in the zinc oxide grain boundaries is 10μm or less, the number of discharges It is remarkably reduced and both are less than 100 times / h. In addition, when a Zn—Al—O compound having a Zn molar ratio larger than the Al molar ratio is present at the zinc oxide grain boundary, the number of discharges is 67 times / h even if the number of discharges is large, and the number of discharges is sufficiently small. It was confirmed that it was possible.

As for individual samples, for example, Sample No. In No. 10, although the zinc oxide particles are large and the grain boundaries are small, it is considered that the number of discharges is slightly increased because the ZnAl ₂ O ₄ particles in the zinc oxide particles are too large. Sample No. In No. 11, it is considered that when ZnAl ₂ O ₄ particles are 10 μm or more, discharge is generated from the starting point. Sample No. No. 13 is thought to be difficult to discharge because Zn—Al—O particles are generated and ZnAl ₂ O ₄ particles are reduced.

10 Zinc oxide particles 20 ZnAl ₂ O ₄ particles 30 Zn—Al—O compound

Claims (2)

A sputtering target material comprising a zinc oxide sintered body,
The density is 5.4 × 10 ³ kg / m ³ or more and 5.6 × 10 ³ kg / m ³ or less,
Containing 1 wt% or more and 3 wt% or less of Al in terms of Al ₂ O ₃ ,
Particle size of ZnAl ₂ O ₄ particles present in the zinc oxide particles is at 3μm or less, the diameter of the ZnAl ₂ O ₄ particles present in the zinc oxide grain boundaries Ri der below 10 [mu] m,
A sputtering target material comprising a Zn-Al-O compound having a Zn molar ratio larger than an Al molar ratio at a zinc oxide grain boundary . Ri Do zinc oxide sintered body, _Al 2 _{O 3} containing 3 wt% or less of Al 1% by weight or more in terms of the particle size of ZnAl ₂ O ₄ particles present in the zinc oxide particles is at 3μm or less, A method for producing a sputtering target material in which the diameter of ZnAl ₂ O ₄ particles present in the zinc oxide grain boundary is 10 μm or less ,
Zinc oxide powder having a primary particle diameter of 500 nm or less and a purity of 99.0% or more produced by the French method is mixed with 1 to 3 wt% of alumina powder having a primary particle diameter of 1 μm or less and purity of 99.0% or more. Mixing, and
Producing a molded body having a density of 50% or more of the theoretical density using the mixed powder;
Firing the molded body at 1350 ° C. or more and 1550 ° C. or less for 10 hours or more,
In the firing step, the temperature drop rate from the firing temperature to 1000 ° C. is set to 50 ° C./h or more.